Without limiting the scope of the invention, its background is described in connection with electrochemical fuel cells, and in particular, to polymeric ionic-diffusion membrane for use in proton exchange membrane fuel cells (hereafter referred to as “PEMFC”) and direct methanol fuel cells (hereafter referred to as “DMFC”). Generally, a fuel cell contains a membrane electrolyte disposed between two electrodes, e.g., a fuel electrode (anode) and an oxygen electrode (cathode). The electrolyte is often a proton conducting polymer membrane formed from a solid polymer. In operation, a fuel cell generates electricity through an oxidation reaction that produces proton and electrons at the anode. The electrons are transferred to the cathode through an external circuit, while the protons are transferred to the cathode through the polymer electrolyte membrane. The environment that the fuel cell is exposed to is harsh and must be able to withstand a wide range of temperatures, while exhibiting electrical and chemical stability. Basically, the fuel cell electrolyte membrane must maintain proton conductivity over a wide range of temperatures.
One common fuel cell electrolyte membrane material includes a perfluorosulfonic acid resin known by the trademark NAFION® which is a sulfonated tetrafluorethylene copolymer). The perfluorosulfonic acid resin is basically a proton exchange resin with sulfonic acid groups that when hydrated the SO3H of a resin branch dissociate to allow proton conductivity. However, at temperatures above 100° C. the ionic resistance of perfluorosulfonic acid resin increases as a result of evaporation of water; moisture allows the operation of PEMFC within the boiling point of water. The limited operating temperature (< about 100° C.) and the need for water to allow proton conduction not only necessitates complex external humidification systems but also leads to a poisoning of the platinum catalyst by trace amounts of carbon monoxide impurity present in the hydrogen fuel. The perfluorosulfonic acid membrane also allows a high permeation of the methanol fuel from the anode to the cathode, referred to as methanol crossover, resulting in a poisoning of the cathode catalyst and consequent performance loss in DMFC. Therefore, design and development of electrolyte membranes that can operate at high temperatures (>100° C.) and low relative humidity in PEMFC and with suppressed or low methanol permeability in DMFC can enhance the commercialization feasibility of the fuel technologies.